A ring laser gyroscope (RLG), sometimes referred to as a ring laser angular rate sensor or short handedly referred to as a ring laser gyro, is used in navigational and guidance systems for a land, air, and/or space vehicles. The RLG utilizes laser beams traveling in opposite directions within a closed loop optical path that are directed by a plurality of reflective devices, such as mirrors. By way of example, an angular orientation of the vehicles is detected with signal processing electronics (e.g., photodiodes), which compares a frequency differential caused by different path lengths of the two beams.
A conventional RLG includes a laser block, a path length control (PLC) driver, and a mirror transducer substrate assembly. The PLC driver generally includes a baseplate, piezoelectric elements, and conductive elements. The mirror transducer substrate assembly generally includes a transducer block with a reflective device, such as a mirror affixed thereto. The structural relationships of the components and operation of the RLG are shown and described in detail in U.S. Pat. No. 5,148,076. In addition, the '076 patent describes one type of configuration for the mirror transducer substrate assembly where a non-uniform outer wall thickness of the transducer block reduces mirror and optical surface deformation. Other aspects generally related to the structural configuration and/or operation of RLGs, such as controllable mirrors, piezoelectric control elements, path length controllers, and the like are described in U.S. Pat. Nos. 4,383,763; 4,488,080; 4,691,323; 5,420,685; 5,960,025; and 6,728,286.
In one embodiment of an RLG, which is shown in FIGS. 1-3, a baseplate 10 includes an actuator plate 12, a flange 14, and an outer rim or sidewall 16. The baseplate 10 includes a hub 18 coupled to and laterally extending from a central portion 20 of the actuator plate 12. The baseplate 10 further includes openings 22 that extend through the sidewall 16, continue around the sidewall/actuator plate interface 24, and extend through the actuator plate 12 itself. The openings 22 allow conductive elements to be routed through the baseplate 10 from a flange side 26 of the baseplate 10. The '076 patent describes one method of routing conductive elements in a PLC driver where the conductive elements make electrical contact with terminal posts via a flex tape and wiring harness.
The openings 22 are electro-discharge machined (EDM) into the baseplate 10. The thermal and mechanical strains created in the baseplate 10 during the EDM process tend to distort, deform, or otherwise warp the baseplate 10. This distortion in the baseplate may be significant enough to cause the mirror transducer substrate assembly, and thus the mirrors, to be out of alignment with a laser optical path within the laser block. In addition or alternatively, this distortion, when combined with the distortion resulting from bonding the PLC driver with the mirror transducer substrate assembly, may cause misalignment of the mirrors. Hence, this distortion of the baseplate 10 is transmitted through the transducer block and results in distortion of the optical contact surface, which is defined as the surface where the mirror is bonded or otherwise affixed to the transducer block.
After the mirror is contacted to the block, the PLC driver is bonded on the backside of the transducer mirror. The block assembly then goes through an initial mirror/block alignment check using a combination of an external laser beam and laser block bending. When it is deemed necessary to make a mirror move, the transducer/mirror assembly is removed from the laser gyro body. Problems can arise when this assembly is removed from the block such as the optical contact area warping. This warping can be severe enough that the mirror/transducer assembly will not go back into contact with the block. When this situation occurs it requires either a re-polish of the optical contact area (with driver attached) or driver removal which results in scrapping the driver assembly. Re-polish of the mirror with a transducer bonded on to achieve a optical contactable flat interface presents the problem of an out of flat mirror once the PLC driver is removed and the mirror is re-used.
Accordingly, a need exists for a baseplate in a PLC driver of an RLG system that overcomes at least some of the aforementioned drawbacks.